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A110428 a(1) = 1 and a(2) = 2. Subsequent terms are generated like this: if a(m) is the last term available -- say a(2) -- then a(m+1) = a(m) * a(m-1), a(m+2) = a(m) * a(m-1) * a(m-2), ..., a(2*m-1) = a(m) * a(m-1) * a(m-2) * ... * a(2) * a(1), a(2*m) = a(2*m-1) * a(2*m-2), and so on. 2
1, 2, 2, 4, 4, 16, 32, 64, 64, 4096, 131072, 2097152, 8388608, 33554432, 67108864, 134217728, 134217728, 18014398509481984, 1208925819614629174706176, 40564819207303340847894502572032, 340282366920938463463374607431768211456 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

By choosing appropriate values for a(1) and a(2), many such sequences can be generated.

LINKS

Table of n, a(n) for n=1..21.

FORMULA

From Petros Hadjicostas, Nov 13 2019: (Start)

a(n) = a(n-1) * a(m) for n >= 3, where m = 2^(p+1) + 2 - n and p is the unique integer such that 2^p < n - 1 <= 2^(p+1), starting with a(1) = 1 and a(2) = 2.

a(A000051(n)) = a(2^n + 1) = a(2^n) for n >= 1.

a(A000051(n) + 1) = a(2^n + 2) = a(2^n + 1) * a(2^n) = a(2^n)^2 for n >= 1.

log[2](a(n)) = A329474(n) for n >= 1. (End)

EXAMPLE

a(3) = a(2)*a(1) = 2. [Now a(3) is the last term available.]

a(4) = a(3)*a(2) = 4.

a(5) = a(3)*a(2)*a(1) = 4. [Now a(5) is the last term available.]

a(6) = a(5)*a(4) = 16.

a(7) = a(5)*a(4)*a(3) = 32.

a(8) = a(5)*a(4)*a(3)*a(2) = 64.

a(9) = a(5)*a(4)*a(3)*a(2)*a(1) = 64. [Now a(9) is the last term available.]

a(10) = a(9)*a(8) = 4096.

a(11) = a(9)*a(8)*a(7) = 131072.

...

a(17) = a(9)*a(8)*...*a(1) = 134217728. [Now a(17) is the last term available.]

a(18) = a(17)*a(16) = 18014398509481984.

[Example extended by Petros Hadjicostas, Nov 13 2019]

MAPLE

a := proc(n) option remember;

`if`(n < 3, [1, 2][n], a(n - 1) * a(2^ceil(log[2](n - 1)) + 2 - n));

end proc;

seq(a(n), n = 1..25); # Petros Hadjicostas, Nov 13 2019

CROSSREFS

Cf. A000051 (index of "available" terms as described above), A050049 (an additive version of this sequence), A329474 (log[2] of this sequence).

Sequence in context: A112869 A086117 A095240 * A076928 A286737 A025557

Adjacent sequences: A110425 A110426 A110427 * A110429 A110430 A110431

KEYWORD

easy,nonn

AUTHOR

Amarnath Murthy, Aug 01 2005

EXTENSIONS

More terms from Joshua Zucker, May 10 2006

STATUS

approved

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Last modified February 9 04:43 EST 2023. Contains 360153 sequences. (Running on oeis4.)